It is now common to track an inventory of various types of articles using computer-readable encoded symbology. Universal product codes are now common on an increasing number of consumer items, and packages and mail are sorted using computer-readable bar codes with increasing frequency.
In many applications, it is desirable to increase the amount of information that may be carried by an encoded marker. This has led to the development of two-dimensional bar codes. By encoding information in two dimensions, such codes may dramatically increase the amount of information-carrying capacity, but present trade-offs which affect accurate reading. Being two-dimensional, these higher capacity codes demand accurate scanning and decoding along two axes, which places further demands on the reading environment, including the types of surfaces upon which such symbology may be placed, lighting conditions, and the amount of processing time required to obtain an accurate reading.
Ideally, the decoding of such two-dimensional markers is preferably performed from a flat surface. In this way, the scanner or reading mechanism if held stable for a long enough period of time, may derive accurate information in a short time, since distortion of the encoded imagery need not be taken into account. However, there are a large class of articles which contain few, if any, flat surfaces, including surgical and scientific instruments, machined parts, tools, ammunition, keys, certain micro electronic components and so forth. In such applications, a new information-bearing marker is required, one that may be read from such articles, even in the event that the marker is placed on a curved or non-planar surface associated with the marker.